This invention relates generally to electrical switches, and, more particularly, to momentary electrical switches of the membrane-type that operate in a normally closed fashion.
Membrane switches have been widely used in recent years for many low-voltage applications. This is due in large part to the switch's simple mechanical construction and its flat front face, which allows convenient placement of descriptive graphics and which seals the switch interior from contamination.
Membrane switches typically include a circuit board having spaced electrical contacts fixed on its upper surface, an overlaying spacer with an aperture aligned with the contacts, and a resilient membrane overlaying the spacer. An electrical contact on the underside of the membrane is normally spaced a predetermined distance above the circuit board contacts, whereby a normally open switch is provided. A downward force applied to the membrane lowers the membrane contact into electrical contact with the spaced circuit board contacts, to short the latter together and thereby close the normally open switch. The circuit board can be either rigid or flexible, depending on the application.
The normally open configuration of the momentary membrane switch described briefly above limits its application. In situations where a normally closed configuration is desired, supplemental electronic circuitry is required.
It should be appreciated from the foregoing that there is a need for an electrical switch having substantially all of the attributes of conventional momentary membrane switches, but operating in a normally closed fashion. The present invention fulfills this need.